This chapter provides an overview the SIP Servlet API, the SIP container, the SIP
servlet environment, SIP classes and methods, and SIP application configuration.

The SIP Servlet API is defined in JSR 116, and describes a standard interface for
programming SIP services and applications. A SIP servlet can be compared with a Java
HTTP servlet but with SIP protocol-related methods. In fact, the SIP Servlet API builds
on the general Servlet API in the same way as the HTTP Servlet API

SIP Servlets are grouped into four categories:

■

User Agent Server: A servlet that acts as a User Agent Server (UAS) receives
incoming requests and sends responses.

■

User Agent Client: A servlet that acts as a User Agent Client (UAC) initiates
outgoing requests and receives responses to these requests.

■

Proxy: A servlet that acts as a proxy receives incoming requests and proxies them
to other end-points (other proxies or a UAS). A proxy servlet will manipulate the
request URI and proxy the request to that destination.

■

Back to Back User Agent: A servlet that acts as a Back to Back User Agent (B2BUA)
acts as both a UAS and UAC on a request. It receives and answers back to one
request (first session) and initiates and receives responses on another request
(second session).